title: Electronic structure of six-coordinate iron(III) monoazaporphyrins.
abstract: The electronic structures of six-coordinate iron(III) octaethylmonoazaporphyrins, [Fe(MAzP)L 2] (+/-) ( 1), have been examined by means of (1)H NMR and EPR spectroscopy to reveal the effect of meso-nitrogen in the porphyrin ring. The complexes carrying axial ligands with strong field strengths such as 1-MeIm, DMAP, CN (-), and (t)BuNC adopt the low-spin state with the (d xy ) (2)(d xz , d yz ) (3) ground state in a wide temperature range where the (1)H NMR and EPR spectra are taken. In contrast, the complexes with much weaker axial ligands, such as 4-CNPy and 3,5-Cl 2Py, exhibit the spin transition from the mainly S = 3/2 at 298 K to the S = 1/2 with the (d xy ) (2)(d xz , d yz ) (3) ground state at 4 K. Only the THF complex has maintained the S = 3/2 throughout the temperature range examined. Thus, the electronic structures of 1 resemble those of the corresponding iron(III) octaethylporphyrins, [Fe(OEP)L 2] (+/-) ( 2). A couple of differences have been observed, however, in the electronic structures of 1 and 2. One of the differences is the electronic ground state in low-spin bis( (t)BuNC) complexes. While [Fe(OEP)( (t)BuNC) 2] (+) adopts the (d xz , d yz ) (4)(d xy ) (1) ground state, like most of the bis( (t)BuNC) complexes reported previously, [Fe(MAzP)( (t)BuNC) 2] (+) has shown the (d xy ) (2)(d xz , d yz ) (3) ground state. Another difference is the spin state of the bis(3,5-Cl 2Py) complexes. While [Fe(OEP)(3,5-Cl 2Py) 2] (+) has maintained the mixed S = 3/2 and 5/2 spin state from 298 to 4 K, [Fe(MAzP)(3,5-Cl 2Py) 2] (+) has shown the spin transition mentioned above. These differences have been ascribed to the narrower N4 cavity and the presence of lower-lying pi* orbital in MAzP as compared with OEP.
authors.affiliation: Department of Chemistry, School of Medicine, Toho University, Ota-ku, Tokyo 143-8540, Japan.
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Nakamura
authors.forename: Akira
authors.initials: A
authors.lastname: Ikezaki
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Ohgo
authors.forename: Takahisa
authors.initials: T
authors.lastname: Ikeue
authors.forename: Saburo
authors.initials: S
authors.lastname: Neya
authors.forename: Mikio
authors.initials: M
authors.lastname: Nakamura
mesh_terms: D001372:Aza Compounds / Q000138:chemical synthesis / Q000737:chemistry; D003486:Cyanides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008665:Metalloporphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry
chemical_list: C417980:4-(dimethylamine)pyridine; D001372:Aza Compounds; D003486:Cyanides; D005290:Ferric Compounds; D008024:Ligands; D008665:Metalloporphyrins; D011725:Pyridines